42 ECONOMIC GEOLOGY OF SILVEETON QUADRANGLE, [bull. 182. 
the thoroughly modern mill of the Camp Bird mine the equipment is 
similar to that which has been found best adapted to the free-milling 
gold ores of California. The ore passes from the crusher directly to 
the stamps, weighing 800 pounds and dropping 90 times a minute. 
The pulp passes through a 40-mesh screen to the amalgamating 
plates, where from 75 to 80 per cent of the value is caught. It is 
then passed through classifiers and over Frue vanners, the latter 
being so arranged that the pulp before being allowed to escape as 
tailings passes over two vanners. The ore commonly run through 
this mill averages from $100 to $200 per ton and is frequently much 
higher. The tailings run from $3 to $5, part of which is recovered 
in a small auxiliary mill. 1 Considering the peculiar character of the 
Camp Bird ore, which will be elsewhere described in this report, this 
showing is rather remarkable. Between mills of this type and the 
more complicated equipment required for treating lower-grade argen- 
tiferous ores there are all gradations, as will appear when each mine 
is described in detail. At the Tomboy mine, which produces a gold 
ore, the ore is crushed by rolls and ground in Huntington mills before 
passing over the plates, no stamps being used. 
The various mills will be described in the detailed accounts of the 
individual mines included in this report. 
The conditions under which the several mines operate differ so 
widely that it is impossible to assign a definite lower limit to the value 
of ores which can be profitably extracted. Ores ranging in value from 
$6 to $12 a ton are perhaps as of low a grade as can be now worked, 
even on a considerable scale and with modern equipment. For many 
of the smaller mines, however, this limit must be doubled. The Re(\ 
Mountain mines were expensive to operate on account of the irregular- 
ity in the disposition of their ore bodies, their corrosive waters, and 
the necessity of pumping and hoisting through shafts. In 1888 the 
New Guston, then beginning operations on an extensive scale, paid 
dividends on ore mined at a cost of $53.50 per ton. The lowest annual 
cost per ton was $9.00 in 1894 on ore worth only $12.80 per ton. Loca- 
tion, power, timber, water, kind of country rock, and character and 
amount of ore form a complex set of factors, which fully accounts for 
the range in the limiting value between workable and nonworkable 
ore. Compared with $1.35 per ton, which in 1894 covered the entire 
cost of mining and treatment of the ore from the Alaska-Tread well 
mine, 2 or the $2.50 to $5 per ton which covers the similar expense in 
many deep California gold mines, the figures given above seem high. 
But the difference is sufficiently explained by the difficulties insepara- 
bly connected with mining in so rugged and elevated a region and by 
the more involved processes required for the treatment of complex 
1 In 1900 a modern cyanide plant was being erected to treat the tailings directly from the mill. 
It is now in operation. 
2 Reconnaissance of the gold fields of southern Alaska, by Or. F. Becker: Eighteenth Ann. Rept. 
U. S. Geol. Survey, Pt. Ill, 1898, p. 64. 
